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Ecology Chapter
14
14.2 Community
Interactions

when organisms live together in an ecological
community they interact constantly.

Three types of interactions
– Competition
– Predation
– Symbiosis
Competition- competing
for resources



occurs due to a limited
number of resources
Resource- any
necessity of life. water,
nutrients, light, food.
Competitive
exclusion principleno two species can
occupy the same niche
in the same habitat at
the same time
Predation



Predation- when
an organism
captures and feeds
on another
organism.
Predator- hunter
Prey- hunted
Symbiosis

Symbiosis- any relationship where
two species live closely together. (3
types)
– Mutualism
– Commensalism
– Parasitism
Symbiosis

Mutualism- both
species benefit
from a relationship.

Lichens (fungus
and Algae)
One example is the lichens, little non-descript patches of stuff you see growing on rocks and tree bark.
This is a symbiosis, consisting of a fungus and an alga. The fungus provides a protective home for the
algae, and gathers mineral nutrients from rainwater and from dissolving the rock underneath. The alga
gathers energy from the sun. There are thousands of species of lichen in the world; actually thousands
of species of fungi with just a few species of algae which can form a partnership with almost any of
them.
Symbiosis

Commensalism –
One member of a
symbiotic
relationship benefits
and the other is
neither helped or
harmed

Ex. Holes used by
bluebirds in a tree
were chiseled out by
woodpeckers after it
has been abandoned
Symbiosis


Parasitism- One
creature benefits
and one creature is
harmed
Ex tapeworm.
Feeds in a humans
intestines absorbing
his/her nutrients.
Relationships: Symbiosis = Living Together
a) commensalism
b) mutualism
c) parasitism
Identify these relationships
Chapter 14.4 –
Population Growth
Patterns
What is a population?
 What is exponential population
growth?
 What happens to a population when it
reaches its carrying capacity?

How many mice are in the following population?
Estimate!
Ready
SET
Go!
How many did you
count?
What is the best way to count
them?
SAMPLING
Population Sampling

Sometimes, the entire population to be
studied is small enough for the researcher
to include the entire population in the study.
– This type of research is called a census study
because data is gathered on every member of
the population.

Usually, the population is too large for the
researcher to attempt to survey all of its
members.
– A small, but carefully chosen sample can be
used to represent the population.
– The sample reflects the characteristics of the
population from which it is drawn
Sampling Methods

There are LOTS ways to sample a
population including:
– Biased sampling, Systematic sampling, Stratified
sampling, Judgment sampling, Quota sampling,
Snowball sampling, Counting method, Hit-ormiss method, etc…

HOWEVER, the most common
methods are:
– Random and non-random sampling
– Each gives you a “best estimate” of
the population size
Population Size

Factors that affect:
– Natality
– Mortality/Fatality
– Immigration
– Emigration
Population Growth Curves

Explain what is happening to the
populations below:
Population Growth Curves

Explain what is happening to the
populations below:
Biotic Potential =
Reproductive Potential
Rate at which a population could grow
if it had unlimited resources
 If a population reached its biotic
potential it would have exponential
growth

The “J” Curve:
Exponential Growth
The “S” Curve: Logistic
Growth
This graph shows
a typical population
growth curve.
Under ideal
conditions a
population would
have a growth with
a slow start, then a
very fast rate of
increase and finally
the growth slows
down and stops.
Population Density

Environmental Limits
on populations

Density-dependent
–
–
–
–
–
Disease
Food
Parasitism
Predation
Competition


Intraspecific
Interspecific

Density-independent
–
–
–
–
–
Temperature
Storms
Floods
Drought
Habitat Disruption
Density Dependent


Here is a dramatic
example of how
competition among
members of one
species for a finite
resource — in this
case, food — caused
a sharp drop in
population.
The graph shows a
population crash; in
this case of reindeer
on two islands in the
Bering Sea.
Inter or Intra?
Density Dependent



This graph shows the effect of interspecific competition on the population
size of two species of paramecia, Paramecium aurelia and Paramecium
caudatum.
When either species was cultured alone — with fresh food added
regularly — the population grew exponentially at first and then leveled off.
However, when the two species were cultured together, P. caudatum
proved to be the weaker competitor. After a brief phase of exponential
growth, its population began to decline and ultimately it became extinct.
The population of P. aurelia reached a plateau, but so long as P.
caudatum remained, this was below the population density it achieved
when grown alone.
Density Independent

This graph shows the
decline in the population of
one of Darwin's finches on
Daphne Major, a tiny (100acre) member of the
Galapagos Islands. The
decline (from 1400 to 200
individuals) occurred
because of a severe
drought that reduced the
quantity of seeds on which
this species feeds. The
drought ended in 1978, but
even with ample food once
again available the finch
population recovered only
slowly.
Limiting Factors

Definition?
What factors would limit
these communities?
Organism Interactions
Limit Populations


Predation
Competition
– Both types


Parasitism
Crowding/stress
The Human Population
Figure 4.10 pg 104
Demography
Vocabulary
Age Structure
 Immigration
 Emigration
 Birth/Death Rate

Age Structure Pyramids

These pyramids compare the age structure of the populations of France
and India in 1984. The relative number (%) of males and females is shown
in 5-year cohorts. Almost 20% of India's population were children — 15
years or less in age — who had yet to begin reproduction. When the
members of a large cohort like this begin reproducing, they add greatly to
birth rates. In France, in contrast, each cohort is about the size of the next
until close to the top when old age begins to take its toll.
Age Structure Pyramids


These population pyramids show the baby-boom
generation in 1970 and again in 1985 (green ovals).
Profound changes (e.g. enrollments in schools and
colleges) have occurred — and continue to occur — in
U.S. society as this bulge passes into ever-older age
brackets.
Chapter 14.5
Ecological Succession

Vocabulary to Know:
– Succession
 Primary
 Secondary
 Pioneer
Species
– Climax Community
Community

All the populations that live together in a
habitat

Habitat is the type of place where
individuals of a species typically live

Type of habitat shapes a community’s
structure
What is Succession &
what causes it?

Changes to a
community

Biotic Factor

Abiotic Factors
2 Types of succession

Primary
– From nothing
– Even the soil must be “created”

Secondary
– From soil
– Disaster can strike and make it start over
Primary Succession
Secondary Succession
Pioneer
Species

Species that colonize barren habitats

Lichens, small plants with brief
life cycles

Improve conditions for other species
who then replace them
Climax Community

Stable array of species that persists
relatively unchanged over time

Succession does not always move
predictably toward a specific climax
community; other stable communities
may persist
The trend of Succession
Pioneer stage  Climax
Community